为了减小激光外差干涉纳米测量的非线性误差，必须明确偏振分光镜(PBS)分光性能非理想对非线性误差的影响机制。推导出非理想情况下偏振分光镜透射率和反射率的激光外差干涉非线性误差模型，建立了偏振分光镜分光性能非理想对非线性误差二次谐波的影响模型。仿真结果表明，偏振分光镜的透射率和反射率非理想对非线性误差的影响为一次谐波，且偏振分光镜分光性能越差，其对非线性误差的影响也越大。在偏振分光镜反射率为0.90的情况下，偏振分光镜透射率从1减小到0.90时，非线性误差由0.62 nm增大到1.24 nm。当存在偏振分光镜旋转角度误差时，偏振分光镜分光性能非理想引起的非线性误差不增加二次谐波分量，但增大了非线性误差一次谐波分量，严重影响非线性误差的大小。当偏振分光镜旋转角度误差为5°时，偏振分光镜透射率从1变为0.90，非线性误差从0.39 nm增大到1.41 nm。

To reduce the nonlinearity of nanometer measurement in laser heterodyne interferometric, the influence mechanics of nonideal splitting performance of polarization beam splitter (PBS) upon nonlinearity must be confirmed. In the paper, nonlinearity model is proposed when polarization transmissivity and reflectivity are not ideal. Model is also proposed to describe how the nonideal splitting performance of PBS influences the second-harmonic nonlinearity. The simulation results show that influence of nonideal polarization transmissivity and reflectivity on nonlinearity is the first-harmonic and the influence will be serious while the splitting performance of PBS gets worse. When reflectivity is 0.90 and transmissivity of PBS reduces from 1 to 0.90, nonlinearity increases from 0.62 nm to 1.24 nm. When the rotation angle error of PBS exists, the second-harmonic nonlinearity caused by the nonideal splitting performance of PBS will be ineffective, but the first-harmonic nonlinearity will increase and the nonlinearity is influenced greatly. It is assumed that the rotation angle error of PBS is 5° and transmissivity of PBS reduces from 1 to 0.90, nonlinearity increases from 0.39 nm to 1.41 nm.